It's designed to circle Mars in low orbit for at least four years and should churn out the most detailed information ever about the planet. In the fall, the orbiter will begin exploring the Martian atmosphere, scanning the surface for evidence of ancient water and scouting for future landing sites to send robotic and possibly human explorers.

The $720 million mission is managed by JPL in Pasadena.

Rewriting the textbooks
Graf predicted that the scientific results of the mission will be extensive. “It will rewrite the science textbooks on Mars,” he said at a post-maneuver news conference.

After a seven-month, 310-million-mile (500-million-kilometer) journey, the orbiter arrived at Mars Friday for the risky orbit insertion phase. Project managers had been nervous because of Mars’ reputation of swallowing scientific probes.

But the Reconnaissance Orbiter performed the move without problem.

As it neared the planet, it fired its main propulsion engines for 27 minutes to slow itself down so that the planet’s gravity could pull it into orbit. At one point during the burn, the spacecraft disappeared behind Mars — as engineers had planned — and was temporarily out of radio contact with controllers.

Mission control was visibly tense as it awaited word from the orbiter, which reappeared and signaled that it had entered into an elliptical orbit that will swing it as close as 250 miles (400 kilometers) above the surface.

"We're there!" one controller said.

“It happened right on the money,” said Dan McCleese, chief scientist for the Mars program at JPL.

Welcome news
The successful mission was welcome news for NASA, which has a mixed record of putting spacecraft into orbit around Mars.

In the last 15 years, NASA has lost two orbiters: the Mars Observer in 1993, just as it was preparing to enter orbit; and the Mars Climate Orbiter in 1999, during the orbital insertion phase.

The Reconnaissance Orbiter is the fourth eye on the Martian sky, joining NASA’s Mars Global Surveyor and Mars Odyssey and the European Space Agency’s Mars Express, which have been mapping the planet the past few years. On the surface, the NASA rovers Spirit and Opportunity, continue their robotic geology missions.

The newest orbiter is loaded with the most advanced scientific instruments ever sent to another planet, including a telescopic camera to photograph the surface in unprecedented detail and radar to probe underground for ice and possible evidence of liquid water.

In advance of the orbital insertion, mission managers checked out the scientific instruments aboard the orbiter, and there were reports that one of the 28 channels on the probe's high-resolution camera was returning bad data. However, a source speaking on condition of anonymity told MSNBC.com that the glitch was not expected to affect science operations.

Over the next seven months, the spacecraft will gradually smooth out its eccentric orbit by dipping repeatedly through Mars' upper atmosphere. The fuel-saving technique, called "aerobraking," was used successfully by Mars Global Surveyor in 1997.

After settling into its proper orbit, Mars Reconnaissance Orbiter will begin an exhaustive two-year scientific survey. Like previous space probes before it, the orbiter will seek evidence of ancient water and other signs that the planet could have been hospitable to life eons ago.

During the mission’s second phase, the orbiter is expected to serve as a communication relay for future probes, such as the Phoenix Mars Scout, which will explore the icy north pole in 2008; and the Mars Science Laboratory, an advanced rover scheduled to launch in 2009.

The Reconnaissance Orbiter’s primary mission is due to end in 2010 — but if the spacecraft stays in good shape, the mission is likely to be extended, as has been the case for the rovers and orbiters currently in operation.